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C104400

DTC C104400 indicates the IPB (Integrated Power Brake) system detects an incomplete or insufficient hydraulic brake line bleeding procedure — Atto 8

Braking System

DTC C104400 indicates the IPB (Integrated Power Brake) system detects an incomplete or insufficient hydraulic brake line bleeding procedure.

The IPB system uses internal pressure sensors to monitor the hydraulic pressure build-up characteristics of each brake wheel cylinder.

When the system detects air in the lines (abnormal compressibility) or identifies an incorrectly executed bleeding procedure, it triggers this fault code and enters fail-safe mode.

This fault restricts ABS/ESP functions, causes abnormal brake pedal travel (spongy pedal), and derates or disables the Automatic Emergency Braking (AEB) function, severely impacting braking safety and driver assistance system performance.

3
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Electronic bleed procedure not performed after brake fluid replacement on Song PLUS DM-i

✓
After bringing the vehicle in for maintenance and brake fluid replacement, the instrument cluster displayed 'Brake System Fault' with DTC C104400. The technician only performed conventional manual pedal bleeding without executing the IPB active bleeding procedure via VDS. They then used the diagnostic tool to access the IPB system and executed the 'Hydraulic Brake Bleeding' special function, completing active bleeding in the right-rear, left-rear, right-front, left-front sequence. The DTC cleared automatically and brake pedal firmness returned to normal.
BYD DTC AI Analysis

Battery discharged during repair, interrupting the exhaust process

✓
Replaced the left rear wheel cylinder due to a brake fluid leak. Did not connect a stabilized power supply during the repair. During brake bleeding, battery voltage dropped to 10.8V, causing the IPB control unit to restart and set C104400, which could not be cleared. Inspection found the IPB internal bleed counter abnormal. Connected a stabilized power supply to maintain voltage above 13V, performed the complete four-wheel brake bleeding procedure again, and executed 'control unit reset' and 'longitudinal and lateral sensor calibration' after bleeding was complete. Fault resolved.
BYD DTC AI Analysis

False exhaust fault due to IPB software false alarm

✓
No prior service history. ABS warning light intermittent. Read fault code C104400; brake pedal felt normal. No brake fluid leaks. Attempted bleed procedure; display indicated "completed" but fault code persisted. Diagnosis found IPB software was early version with a bug. Solution: Upgraded IPB control unit software to latest version (via BYD OTA or offline programming). Fault code cleared after upgrade. No recurrence after one week of monitoring.
Other Atto 8 Fault Codes
B1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.